The present invention relates to devices for transporting objects (e.g., workpieces) which consist (entirely or in part) of ferromagnetic material so that they can be lifted, attracted and transported by an electromagnet. More particularly, the invention relates to improvements in lifting electromagnets, especially for use in or in conjunction with machine tools, e.g., to deliver workpieces to and to remove workpieces from the treating stations of material removing machines.
It is known to use lifting electromagnets for the transport of ferromagnetic substances, e.g., scrap metal. It is also known to use electromagnets as a means for feeding workpieces to and for removing workpieces from the work processing stations of machine tools. Proper operation of such electromagnets is ensured only if they can predictably grip, lift and transfer selected workpieces, and they should be sufficiently versatile to be capable of properly engaging workpieces having different diameters, lengths and/or other parameters. For example, if a lifting electromagnet is used to transfer workpieces from a container to the work treating station of a machine, the electromagnet should be capable of properly grasping randomly or uniformly distributed workpieces which are confined in the container, of delivering such workpieces to the treating station and leaving the thus delivered workpieces at the treating station or transferring finished workpieces from the treating station to a different location, e.g., onto a conveyor which delivers the treated workpieces to a further machine, to a different container, to storage or to another destination.
Conventional lifting electromagnets are incapable of engaging and transporting differently configurated and/or dimensioned workpieces. For example, a first lifting electromagnet is required to lift largediameter rods, and a different second electromagnet is used for the lifting of rods having relatively small diameters. The same holds true if a set of relatively short workpieces is followed by a set of longer or much longer workpieces or if a batch of lightweight workpieces is followed by a batch of much heavier workpieces. An electromagnet which can properly lift a relatively short workpiece may not be suited for the lifting of much longer workpieces because a longer workpiece is likely to change its orientation (e.g., by tilting) and to become dispengaged from the poles of the electromagnet. Tilting moments are likely to develop if the electromagnet engages a long workpiece at a locus which is remote from the center (i.e., not midway between the longitudinal ends) of the workpiece. Such unexpected or unintentional descent of a long and possibly heavy metallic or like workpiece is likely to interrupt the operation of a production line, to cause damage to the machine and/or to injure the attendants.